The invention relates to a cooking appliance having a plate made of a material transparent to thermal radiation, such as glass-ceramic, glass, ceramic, or a similar material, for cooking, baking, frying, and/or keeping warm, having adjustable heat sources distributed under, in, or on the plate, heated by means of direct or indirect heat transfer, electrically, and/or by gas and/or by other heating means, in which the plate possesses at least two types of heat sources which use different kinds of heat transfer.
At present, various hob-type or stovetop systems (hereinafter "hobs") are known commercially:
(1) Hobs having atmospheric open burners whose covering can comprise metal, e.g., steel, or steel-enamel or glass. The advantages of these appliances are in their ability to operate with a very short response time and fine adjustability of the heat output. The immediate visual recognition of a flame can also be advantageous for avoiding burn injuries when using this type of hob. A further compelling reason for the acquisition of such cooking appliances is also the very favorable price.
There are nevertheless disadvantages in the areas of appearance, diversity of design, and also, in particular, in ease of use and cleaning. Neither will a hob of this construction ever provide, as a work surface, an additional usable space, e.g., for the preparation of meals or for the safe setting down of, e.g., foodstuffs, pots, or pans.
(2) Hobs having a level covering over the entire surface, in particular of glass-ceramic, whose heat sources are arranged under the plate and which, according to the current state of the art, can be heated electrically by heating coils or by infrared radiant gas burners. Advantages associated with these hobs are their attractive appearance and their diversity of design, which can be ideally matched to a large variety of decor and color schemes in any particular kitchen layout. Cleaning of the level plate is also easy and problem-free, and the plate can also be used as an additional work surface or place for safely setting down, e.g., pans. The temperature distribution at low temperatures, as are required, for example, for keeping food warm, is appreciably more uniform in this kind of cooking area which is not heated directly by a flame, and the peak temperatures occurring are very much lower. Disadvantages which should be mentioned here are a delayed emission of heat to the food to be heated and a correspondingly lower energy efficiency of the heating means, and hence also a longer heat-up time for the food. In addition, the price of these hobs is considerably higher in comparison with the metal hob with open burners.
(3) A further variant is an electric cooker with a metal covering which, in contrast to the above-mentioned covering over the entire surface has individual discrete raised cooking areas, mostly of black cast iron. Its disadvantages are, inter alia, the appearance and, again, the poor ease of cleaning. Also, even up to very high temperatures, visual recognition whether a cooking area is presently being heated is impossible. Its advantage is its relatively low price.
DE 30 49 491 C2, claims a cooker whose top surface is formed of a single, level heat-transfer plate with a continuous closed surface, in particular, a glass-ceramic plate, under which is arranged at least one radiant gas burner, and at least one electric radiant element is arranged under the heat-transfer plate outside the gas cooking region, beside, and/or in the simmering warm-plate region.
DE 30 49 491 C2, thus, discloses radiant gas burners, in addition to electrically supplied radiant elements under a heat-transfer plate having a continuous closed surface.
FR 2 626 946 A1 discloses a cooker in which there is an electric radiant element under a glass-ceramic covering and, in addition, normal gas burners with open flame are provided.
FR 2 626 964 A1, thus, discloses different types of heat sources, namely, electric radiant elements next to normal gas burners, the glass-ceramic plates here in each case covering only the single electric radiant element and do not form a continuous plate with heat sources distributed under, in, or on it.
DE 37 15 126 C2 discloses a cooking area especially for a burner in a mobile home, with a cooking area frame and an intermediate bottom design, whose object is to avoid disturbing deformations of the intermediate bottom and, at the same time, to achieve good heat insulation of the cooking area.
U.S. Pat. No. 1,764,718 describes a device for improved air supply in overlapped gas burners.
None of these documents discloses a cooking device which exhibits at least two types of heat sources using different kinds of heat transfer, in which the heat sources are all heated by gas.